3 COMMON QUESTIONS ABOUT DRS PREFERENTIAL VM-HOST AFFINITY RULES
On a regular basis I receive questions about the behavior of DRS when dealing with preferential VM to Host affinity rules. The rules configured with the rule set “should run on / should not run on” are considered preferential. Meaning that DRS prefers to satisfy the requirements of the rules, but is somewhat flexible to run a VM outside the designated hosts. It is this flexibility that raises questions; lets see how “loosely” DRS can operate within the terms of conditions of a preferential rule: Question 1: If the cluster is imbalanced does DRS migrate the virtual machines out of the DRS host group? DRS only considers migrating the virtual machines to hosts external to the DRS host group if each host inside the group is 100% utilized. And if the hosts are 100% utilized, then DRS will consider virtual machines that are not part of a VM-Host affinity rule first. DRS will always avoid violating an affinity rule Question 2: When a virtual machine is powered on, will DRS start the virtual machine on a host external to the DRS host group? By default DRS will start the virtual machine on hosts listed in the associated Host DRS group. If all hosts are 100% utilized – or – if they do not meet the virtual machine hardware requirements such as datastore or network connectivity, then DRS will start the virtual machine on a host external to the Host DRS group. Question 3: If a virtual machine is running on a host external to the associated host DRS group, shall DRS try to migrate the virtual machine to a host listed in the DRS host group? The first action DRS triggers during an invocation is to determine if an affinity rules is violated. If a virtual machine is running on a host external to the associated Host DRS group then DRS will try to correct this violation. This move will have the highest priority ensuring that this move is carried out during this invocation.
MIGRATING DATASTORE CLUSTERS BY CHANGING STORAGE PROFILES IN A VCLOUD
vCloud director 5.1 supports the use of both storage profiles and Storage DRS. One of the coolest features and unfortunately relatively unknown is the ability to live migrate virtual machines between datastore clusters by changing the storage profile in the vCloud director portal. In my lab I’ve set up a provider vDC that contains two compute clusters. Each compute cluster connects to two datastore clusters. Datastore Cluster “vCloud-SDC-Gold” is compatible with the VM storage profile “vCloud-Gold-Storage”, while Datastore Cluster “vCloud-SDC-Silver” is compatible with the VM storage profile “vCloud-Silver-Storage”. When creating a vApp the default storage profile of the organization vDC is applied to the vApp and all its virtual machines. In this case, the VM storage profile Gold is applied to all the virtual machines in the vApp. You can determine which VM Storage Profile is associated with the virtual machine by selecting the properties of the virtual machine in the “My Cloud” tab. Please note that vCloud Director does not show the VM Storage Profile at the vApp level! By selecting the drop-down box, all storage profiles that are associated with the organization vCD are displayed. By selecting the Storage Profile “vCloud-Silver-Storage” vCloud Director determines that the virtual machine is stored on a datastore that is not compatible with the associated storage profile. In other words the current configuration is violating the storage level policy. To correct this violation, vCloud director instructs vSphere to migrate the virtual machine via Storage vMotion to a datastore that is compatible with the VM storage Profile. In this case the datastore cluster “vCloud-DSC-Silver” is selected as the destination. Storage DRS determines the most suitable datastore by using its initial placement algorithm and selects the datastore that has the most amount of free space and the lowest I/O load. To demonstrate the feature, I selected the virtual machine “W2K8_R2-SP1”. The VM storage profile “vCloud-Gold-Storage” is applied and Storage DRS determined that the datastore “nfs-f-vcloud03” of the datastore cluster “vCloud-DSC-Gold” was the most suitable location. By changing the Storage Profile to “vCloud-Silver-Storage” vCloud director instructed vSphere to migrate it to the datastore cluster that is compatible with the newly associated VM storage profile. When logging into the vCenter server managing the ESXi hosts the following task is running: After the task is complete, vCenter shows that the virtual machine is now stored on datastore “nfs-f-vcloud06” in the datastore cluster “vCloud-DSC-Silver”. The power of abstraction The abstraction layer of vCloud Director makes this possible. When changing the storage profile directly on the vSphere layer, nothing happens. vSphere will not migrate the virtual machine to the appropriate datastore cluster that is compatible with the selected VM storage profile. Useful for stretched clusters? The reason why I was looking into this feature in my lab is due to an conversation with my esteemed colleagues Lee Dilworth and Aidan Dalgleish. We were looking to an alternative scenario for a stretched cluster. By leveraging the elastic vDC feature of vCloud director, a seperate DRS cluster is created in each site. Due to the automatic initial placement engine on the compute level, we needed to find a construct that can provide us a more deterministic method of virtual machine placement. We immediately thought of the VM profile storage feature. Create two datastore clusters, one per site and associate a profile storage based on site name to the respective datastore clusters. When creating the vApp, just select the site-related Storage Profile to place the virtual machine in a specific site. Due to the compatibility check, vCloud Director determines that in order to be compliant with the storage profile it places the virtual machine on the compute cluster in the same site. For example, if you want to place a virtual machine in site 1, select the VM storage Profile “site 1”. vCloud director determines that the virtual machine needs to be stored in datastore cluster “DSC-Site-1”. The compute cluster Site-1 is the only compute cluster connected to the datastore cluster, therefor both the compute and storage configuration of the virtual machine is stored in Site 1. This configuration works perfect if you want to simplify initial placement if you have multiple sites/locations and you always want to keep the virtual machine in the same site. However this solution might not be optimal for a Stretched cluster configuration where failover to another site is necessary. Connectivity to all datastores necessary As this feature uses storage vMotion instead of cross-host/datastore vMotion, means that the cluster needs to be connected to both datastore clusters. When selecting the different storage profile, the storage state is migrated to another datastore cluster. However it doesn’t move the compute state of the virtual machine. This means that storage is moved to site B, while the compute state is still in Site A. vCloud director does not provide an option to migrate the virtual machine to a different compute cluster within the provider vDC. You can either solve it by logging into the vCenter server that manages the ESXi hosts and manually vMotion the virtual machines to cluster in Site B, or power-off the virtual machine in vCloud Director, then change the storage profile and power-on the virtual machine. Both “solutions” are not very enterprise-level scenario’s therefor I think this is not yet suitable as a stretched cluster configuration
VMWORLD 2013 - CALL OF PAPERS DEADLINE ENDS TODAY
Just a reminder here on submitting VMworld sessions. The deadline is coming up quickly. If you haven’t submitted yet, you have still some hours left to submit a Session Proposal for VMworld 2013. Submit your session today!
VMOTION OVER LAYER 3?
This question regularly pops up on twitter and the community forums. And yes it works but VMware does not support vMotion interfaces in different subnets. The reason is that this can break functionality in higher-level features that rely on vMotion to work. If you think Routed vMotion (vMotion interfaces in different subnets) is something that should be available in the modern datacenter, please fill out a feature request. The more feature requests we receive; the more priority can be applied to the development process of the feature.
SAVING A RESOURCE POOL STRUCTURE WEB CLIENT FEATURE NOT SUITABLE FOR VCD ENVIRONMENTS
Last week I published the article “Saving a Resource Pool Structure” describing the RP-tree backup and restore feature of vSphere 5.1 web client. Multiple people immediately asked if the feature keeps the Managed Object Reference ID (MoRef) of the resource pools identical when it restores the resource pool tree? This is important for vCloud Director as it creates a relationship between vCloud Director objects organization vCD and the vSphere level resource pool. vCloud Director ties the org vCD UUID with the vSphere resource pool Moref id within vCD database. For more information read Chris his post: “Gotcha: Disabling VMware DRS with vCloud Director”. Unfortunately the feature just captures the old tree structure and rebuilds a new tree structure. I tested it by using William Lam’s custom Perl script called moRefFinder.pl. Please visit Williams site to download his script. Then I proceeded to backup and restore the resource pool tree. vCenter showed the follow commands being processed. Then I checked if the MoRef ID was the same as prior to disabling DRS. As shown, the current MoRef ID of the “00-Infra-mgmt” resource pool is 137 contrary to MoRef ID of 129 before disabling DRS. Therefor you should not use this feature when planning to backup and restore the resource pool used by VCD for its organization vCD structures.
SAVING A RESOURCE POOL STRUCTURE
During a troubleshooting exercise of a problem with vCenter I needed to disable DRS to make sure DRS was not the culprit. However a resource pool tree exisited in the infrastructure and I was not looking forward reconfiguring all the resource allocation settings again and documenting which VM belonged to which resource pool. The web client of vSphere 5.1 has a cool feature that helps in these cases. When deactivating DRS (Select cluster, Manage, Settings, Edit, deselect “Turn ON vSphere DRS”) the user interface displays the following question: Backup resource pool tree Click “Yes” to backup the tree and select an appropriate destination for the resource pool tree snapshot file. This file uses the name structure clustername.snapshot and should the file size be not bigger than 1 or 2 KB. Restore resource pool tree When enabling DRS on the cluster, the User interface does not ask the question to restore the tree. In order to restore the tree, enable DRS first and select the cluster in the tree view. Open the submenu by performing a right-click on the cluster, expand the “All vCenter Actions” and select the option “Restore Resource Pool Tree…” A window appears and click browse in order to select the saved resource pool tree snapshot and click on OK vCenter restores the tree, the resource pool settings (shares, reservations limits) and moves the virtual machines back to the resource pool they were placed in before disabling DRS. If you want to save the complete vCenter inventory configuration I suggest you download the fling “InventorySnapshot”. Update: If you want to use this tool to backup and restore resource pool trees used by vCloud Director, please read this article: Saving a Resource Pool Structure web client feature not suitable for vCD environments
ELASTIC VDC AND HOW TO SPAN A PROVIDER VDC ACROSS MULTIPLE DRS CLUSTERS
vCloud director 5.1 provides the ability to create elastic vDC which allows an organization vDC to consume resources from multiple DRS clusters. By having the provider vDC abstract the resources from multiple DRS clusters, its simpler to grow capacity when needed. Before elastic vDC, a new provider vDC and Org vDCs needed to be created when an org vDC wanted to grow beyond the capacity of the provider vDC. With Elastic vDC you just add new clusters when needed and allow the Provider vDC to manage initial placement of vApps. During research of elastic vDCs I discovered that the way to span a provider vDC isn’t that intuitive. In order to save you some time, here are the steps to create a provider vDC that spans multiple DRS clusters. Create a Provider vDC, give it a name and select the highest supported hardware version. If you run a homogenous environment with solely 5.1 ESX hosts I highly recommend changing it to Hardware Version 9. If the clusters run different ESX versions, lower the hardware version to the appropriate supported level. Please note that the provider vDC is responsible for initial placement of the vApp. It will place the vApp on the cluster that contains the most available “unreserved” compute resources and storage resources. It is possible that vApps of the same organization run on different ESX versions. Select Resource pool. This screen is a little bit ambiguous. The user interface “talks” about resource pools, but that doesn’t mean you cannot select a complete DRS cluster for consumption by the provider vDC. A DRS cluster is in essence a resource pool, the root resource pool for all its child resource pools. So don’t worry if you want to select an entire cluster, in matter of fact, when you select the vCenter it shows the DRS clusters as well as the resource pools. In this example, the vCenter contains two DRS clusters; vCloud-Cluster1 and vCloud-Cluster2. The DRS cluster vCloud-Cluster2 contains a resource pool called RP1. Unfortunately the user interface does not use any icons to differentiate between clusters and resource pools, but shows a vCenter path notation. As RP1 is the child resource pool of vCloud-Cluster2, the vCenter path is as follows: vCloud-Cluster2/RP1. Unfortunately the interface only allows to select a single resource pool or cluster, therefor I select the vCloud-Cluster1 and select next. Select an appropriate Storage profile and click on next. The ready to complete screen displays an overview of your selected configuration. Click on Finish to create the Provider vDC. At this point in time, the provider vDC maps to only one DRS cluster. To add additional clusters, go to the Manage and Monitor tab and select Provider vDCs. Click on the provider vDC and select the resource pools tab Click on the green plus icon to add another DRS cluster. The attach resource pool window is displayed and you can select another cluster from the same vCenter as the primary cluster. Please note that a provider vDC can only span clusters managed by the same vCenter server. Click on Finish to add the DRS cluster to the provider vDC. The Provider vDC is now able to provider resources from multiple DRS clusters. In vCloud Director 5.1 both the Pay-as-You-Go and Allocation Pool model org vCD are able to consume resources from an elastic vDC. In order to allow the Allocation Pool model to leverage an Elastic vDC changes needed to be made. Massimo Re Ferrè wrote an extensive post about the changes of the different allocation models in vCloud director 5.1.
WOULD YOU BE INTERESTED IN STORAGE-LEVEL RESERVATIONS?
In todays world it’s quite common to virtualize higher priority / tier-1 applications and services. These applications and services are usually subject to service level agreements that typically include requirements for strong performance guarantees. For the compute resources (CPU and Memory) we are relying on the virtualization layer to give us that resource allocation solution by setting reservation, shares and limits. You might want to ensure that the storage requirements of these virtual machines are met and when contention for storage resources occurs these workloads are not impacted. Today vSphere offers Storage I/O Control (SIOC) to allocates I/O resources based on the virtual machine priority if datastore latency is exceeded. Shares identify priority while limits restrict the amount of IOPS for a virtual machine. Although these are useful controls it does not provide a method to define a minimum amount of IOPS that is available all the time to the application. Providing lots of shares to these virtual machines can solve help to meet the SLA, however continuously calculating the correct share value in a highly dynamic virtual datacenter is cumbersome and complex job. Storage level reservations Therefore we are working on Storage level reservations. A storage reservation allows you to specify a minimum number of IOPS that should be available to the virtual machine at all times. This allows the virtual machine to make minimum progress in order to comply with the service level agreement. In a relative closed environment such as the compute layer its fairly easy to guarantee a minimum level of resource availability, but when it comes to a shared storage platform new challenges arise. The hypervisor owns the computes resource and distributes it to the virtual machine it’s hosting. In a shared storage environment we are dealing with multiple layers of infrastructure, each susceptible to congestion and contention. And then there is the possibility of multiple external storage resource consumers such as non-virtualized workloads using the same array impacting the availability of resources and the control of distributing the resources. These challenges must be taken into account when developing storage reservations and we must understand how stringent you want the guarantee to be. One of the questions we are dealing with is whether you would like a strict admission control or a relaxed admission control. With strict admission control, a virtual machine power-on operation is denied when vSphere cannot guarantee the storage reservation (similar to compute reservations). Relaxed admission control turns storage reservations into a share-like construct, defining relative priority at times where not enough IOPS are available at power-on. For example: Storage reservation on VM1 = 800 and VM2 = 200. At boot 600 IOPS are available; therefore VM1 gets 80% of 600 = 480, while VM2 gets 20%, i.e. 120 IOPS. When the array is able to provide more IOPS the correct number of IOPS are distributed to the virtual machines in order to to satisfy the storage reservation. In order to decide which features to include and define the behavior of storage reservation we are very interested in your opinion. We have created a short list of questions and by answering you can help us define our priorities during the development process. I intentionally kept the question to a minimum so that it would not take more than 5 minutes of your time to complete the survey. Disclaimer As always, this article provides information about a feature that is currently under development. This means this feature is subject to change and nor VMware nor I in no way promises to deliver on any features mentioned in this article or survey. Any other ideas about storage reservations? Please leave a comment below. The survey is closed, thanks for your interest in participating
HELLO WORLD! AGAIN
During my holiday, frankdenneman.nl got some unwanted attention. I’m currently in the process of rebuilding the site. Stay tuned for new updates!
WOW, VOTED NUMBER 2 OF TOP VIRTUALIZATION BLOGS!
Voted number 2 of top virtualization blogs As many other IT-addicts, the first thing I do is pick up my phone to see what’s new on twitter, google+ and facebook and to my surprise I received a lot of direct messages and mentions congratulating on taking the second spot on the top 25 virtualization blog list. WOW talk about excitement! From being drowsy to uber-hyped in under a millisecond. Thanks for voting me! I really appreciate the recognition. I love to blog and write articles and when I’m not researching I’m thinking of topics I can cover. Reaching the number 2 spot proves I’m doing something you all like. But actually I want to thank you for taking the time to vote on any of the top 25 blogs. Everybody spends a great deal of time researching and writing articles, getting votes is a great way to receive acknowledgement for your hard work. A big thank you goes out to Eric for organizing this competition again. Awesome work and thanks for putting in all the effort. Viewing the stats it shows that this event is becoming more and more an industry event, organized by community members for community members. Great stuff. John, David, Simon similar to last year, great vChat. A delight to watch! BTW, thank you for the compliments! It’s always cool to hear some background details of the top 25 bloggers. I encourage you to watch the special vChat it’s great entertainment! Congrats to Duncan for taking the number 1 spot. Well deserved! I know how much effort you put into the blog. Outstanding stuff. Congrats to the rest of the top 25 and a special congrats goes out to Cormac. Well deserved to enter in the top 10. If you are on twitter make sure you follow each and everyone of the top 25. These guys are a special bunch, all passionately about virtualization and great bunch of people in general. Here is the list of the top 25 on twitter: